Low turbulence fluid management system for endoscopic procedures

ABSTRACT

The present invention provides a system and a method for distending a body tissue cavity of a subject by continuous flow irrigation by using two positive displacement pumps, such as peristaltic pumps, one pump on the inflow side and another pump on the outflow side, such that the amplitude of the pressure pulsations created by a the said positive displacement pumps inside the tissue cavity is substantially dampened to almost negligible levels. The present invention also provides a method of reducing the frequency of the said pressure pulsations. The present invention also provides a method for accurately determining the rate of fluid loss, into the subject&#39;s body system, during any endoscopic procedure without utilizing any deficit weight or fluid volume calculation, the same being accomplished by using two fluid flow rate sensors. The present invention also provides a system of creating and maintaining any desired pressure in a body tissue cavity for any desired cavity outflow rate. The system and the methods of the present invention described above can be used in any endoscopic procedure requiring continuous flow irrigation few examples of such endoscopic procedures being hysteroscopic surgery, arthroscopic surgery, trans uretheral surgery, endoscopic surgery of the brain and endoscopic surgery of the spine.

FIELD OF INVENTION

The present invention relates to a system for distending body tissuecavities of subjects utilizing continuous flow irrigation duringendoscopic procedures. The system and the methods of the presentinvention described above can be used in any endoscopic procedurerequiring continuous flow irrigation few examples of such endoscopicprocedures being hysteroscopic surgery, arthroscopic surgery, transuretheral surgery (TURP), endoscopic surgery of the brain and endoscopicsurgery of the spine. The proposed invention can also have certainuseful non medical applications.

BACKGROUND OF THE INVENTION

Endoscopic surgery is becoming increasingly popular because of thefollowing reasons:

-   (a) it is a minimally invasive form of surgery,-   (b) it avoids large incisions over the skin and muscle,-   (c) it is associated with less pain,-   (d) there is a relatively less requirement of blood transfusions and-   (e) the patients can return back to normal work relatively early    with minimal loss of working days.

While in the corresponding open conventional surgeries a relativelylarge body part consisting of skin and muscle needs to be cut in orderto gain access to an underlying body tissue cavity, in endoscopicsurgery instead of cutting body structures like skin and muscle anendoscope is introduced into the body cavity via the natural opening ofa cavity, if such exists, or alternatively a minute hole is made in thewall of the cavity through which the endoscope is introduced tovisualize the interior of the body tissue cavity and to perform major orminor endoscopic surgical procedures. For this reason endoscopic surgeryis also sometimes called ‘key hole’ or ‘minimal access surgery’. Besidesreducing the pain associated with surgery, endoscopic surgery also helpsin reducing the medical expenses.

Endoscopic Surgery is Primarily Related to a Tissue Cavity:

All endoscopic surgeries are carried out on a existing body cavity whichis distended or ‘ballooned up’ by a suitable distending apparatus whichpermits the inner lining of the said tissue cavity to be visualized bythe help of an endoscope. Though multiple endoscopic procedures havebecome established as the preferred surgical modality but still there isimmense scope of increasing the safety and efficiency of the suchexisting endoscopic procedures by improving upon the existing techniquesand apparatus used for distending body tissue cavities. Hysteroscopy,arthroscopy, TURP (transuretheral resection of the prostate), endoscopicsurgery of the brain and endoscopic surgery of the spine are few of theroutinely performed endoscopic procedures and the organs related to suchsurgeries being uterus, human joints, bladder, brain and the spinerespectively. The list of endoscopic surgeries is long, ever increasingand there is hardly any body organ or organ system to which the benefitsof endoscopy have not been extended.

Tissue Cavitiy is Initially Collapsed in its Natural State:

In the natural state tissue cavities are collapsed structures and thecavity walls are in apposition with each other as if kissing each other.Thus if an endoscope is introduced in such a collapsed cavity noendoscopic visualization is possible unless the cavity is ballooned upby filling it with a transparent fluid or a gas. Such ballooning of atissue cavity is technically termed as ‘cavity distension’. Noendoscopic procedure can be performed without an efficient cavitydistending system and no endoscopic procedure should be attemptedwithout a safe distending system because unsafe tissue cavity distendingmeans can lead to extreme human morbidity and even the death of apatient and such grim realities shall be discussed in the later sectionsof this manuscript. Cavity distension provides both endoscopicvisualization and mechanical distension which is necessary for themovement of endoscopic instruments.

Continuous Flow Irrigation:

In the present invention, the Inventors are focused on a system fordistending body tissue cavities for those endoscopic procedures in whichthe cavity needs to be distended by utilizing continuous flow irrigationonly. Here, the term ‘continuous flow irrigation’ means that fluidsimultaneously enters and escapes from a tissue cavity via separateentry and exit points, as a result of which a positive fluid pressure iscreated inside the tissue cavity which distends the cavity.

The Need for Continuous Flow Irrigation:

Any tissue cavity can be easily distended in a ‘static manner’ by simplypushing fluid via a single inflow tube inserted into the cavity and inthis manner a desired cavity pressure can be developed and alsomaintained. For example, a cavity can be distended by pressing on thepiston of a simple syringe filled with fluid with the outlet end of thesyringe being connected to the cavity by a tube. Alternatively a fluidfilled bottle may be elevated to a suitable height and under theinfluence of gravity fluid from such bottle may be allowed to enter thecavity via a tube connecting the said bottle to the cavity and in thismanner a desired static pressure can be developed and also maintained.Though it is very easy to achieve distension by the said static manner,it is not a practical solution because blood and tissue debris which areinvariably released from the fragile cavity inner lining mix with thedistending fluid and endoscopic vision gets clouded within a few secondsor a few minutes. Thus continuous flow irrigation is needed toconstantly wash away blood and tissue debris in order to maintainconstant clear endoscopic vision.

Cavity Pressure and Cavity Flow Rate:

It is obvious that cavity fluid pressure and the flow rate through thecavity are the two basic parameters associated with all continuous flowirrigation systems.

An Efficient Distending System:

The Inventors believe that an efficient distending system is the onewhich provides a predictably continuous clear visualization and apredictably stable mechanical stabilization of the cavity walls. Inorder to achieve this the Inventors believe that a suitable stableconstant precise cavity pressure and a suitable stable precise cavityflow rate have to be created and maintained in a predictable andcontrolled manner. The cavity pressure should be adequate so that visionis not clouded by oozing of blood and enough mechanical separation ofthe cavity walls occurs to allow the movement of the endoscope.Similarly, the cavity flow rate should be adequate enough to constantlywash away blood and tissue debris in order to allow clear vision. Manyprior systems utilize a peristaltic pump over the inflow and or theoutflow side and these peristaltic pumps create pressure pulsationswhich are then transmitted to the tissue cavity. Such pressurepulsations are undesirable and the main aim of the present invention isto dampen such pressure pulsations.

A Safe Distending System:

An efficient distending system as explained in the previous paragraphneed not also be a safe distending system. In this regard, the Inventorswould like to highlight that if the cavity pressure rises above theprescribed safe limits excessive fluid intravasation may occur or thecavity may even burst. Fluid intravasation is a process by which theirrigation fluid enters into the patient's body system through thecavity walls and may cause significant danger to the patient's lifeincluding death. Thus a safe distending system is one which prevents orminimizes fluid intravasation and allows the surgeon to accurately knowthe instantaneous real time rate of fluid intravasation into thepatient's body system.

No Prior Art is Absolutely Safe:

Many different types of uterine distending systems are known and arebeing commercially marketed by many different companies but none ofthese systems can be considered to be absolutely safe for the patient.This fact has been clearly stated in the ‘Hysteroscopic Fluid MonitoringGuidelines proposed by the Ad Hoc Committee on Hysteroscopic FluidGuidelines of the American Association of Gynecologic LaproscopistsFebruary 2000 (Loffler F D, Bradley L D, Brill A I et al: Hysteroscopicfluid monitoring guidelines. The journal of the Americal Association ofGynecologic Laproscopists 7(1): 167-168, 1994) where the authors clearlyand explicitly state “fluid pumps for low-viscosity media are aconvenience and do not guarantee safety”. The present invention aims atproviding a distending system which is both safer and more efficient incomparison to all the prior art systems.

Basic Physics of Cavity Distension:

Although, a person skilled in the art may know it, the Inventors wouldlike to provide a brief description of the basic physics of cavitydistension. Filling the tissue cavity with fluid enables distension ofthe same. Initially more fluid is pumped in than the amount which isextracted from the cavity and ultimately the inflow rate is fixed at alevel where a somewhat desired cavity pressure and distension isachieved. It may be possible to accurately maintain the desired pressureand distension in the case of a rigid cavity, for example a cavity madeof steel.

However, the body tissue cavities are not rigid because they aredistensible and also have some element of elasticity. Thus a distendedtissue cavity in its attempt to constantly revert back to its naturalcollapsed state reacts by exhibiting physiological contractions of thecavity wall which generally leads to variations in the cavity pressurewhich ultimately culminates in irregular movement excursions of thecavity walls. In a static system the said movement excursions may be sominute that they may even go unnoticed. However in a dynamic system suchthat being created during an endoscopic procedure, the saidphysiological cavity wall contractions may cause the cavity to expel outits entire fluid content thus leading to a surgically dangerous largemagnitude movement excursion of the cavity wall. Because of thesereasons it is extremely difficult to maintain the cavity pressure andcavity distension in a predictably stable fashion.

Further, the inflow tube, the out flow tube and the endoscope alsoinvariably move and shake during surgery which leads to variations influid flow resistance which is also manifested in the form of variationsin the cavity pressure. The cavity pressure variations occurring as aresult of cavity wall contractions and the mechanical movement of thetubes and the endoscope tend to occur again even if they are correctedonce because it is impossible to prevent the physiological cavity wallcontractions and the mechanical movements of the irrigation circuit.Thus, the said cavity pressure variations shall continue to occur evenafter multiple repeated corrections.

Thus, till date the surgeon was only left with two options, either toignore the said cavity pressure variations by not correcting them, or toexternally and actively correct such pressure variations. The Inventorshave noticed that any attempt to externally and actively correct thesaid cavity pressure variations leads to an undesirable turbulenceinside the cavity and also tends to amplify the resultant movementexcursions of the cavity walls. Thus there is a grave need to provide asystem which can maintain an almost constant and stable cavity pressureeven in the presence of the said physiological cavity contractions andthe mechanical movements in the irrigation circuit.

Brief Description of an Endoscope:

Prior to describing the basic layout of a continuous flow irrigationsystem the basic structure of an ‘endoscope’ needs to be described.Endoscope is a cylindrical tube having an outer diameter ranging between3 to 9 mm approximately. A typical endoscope has four channels. Onechannel is meant to pass a fibereoptic telescope while endoscopicinstruments are negotiated through a second instrument channel. A thirdchannel also known as the inflow channel is used for pushing irrigationfluid into a tissue cavity, the proximal end of this channel ending in ametal adaptor known as the inflow port while the distal end of thisinflow channel opens near the tip of the endoscope. The inflow port isconnectable to an inflow tube which carries sterile irrigation fluidfrom a fluid source reservoir. A fourth channel also known as the outflow channel is meant for extracting waste fluid out of the cavity, theproximal end of this channel ending in a metal adaptor known as theoutflow port while the distal end of this outflow channel opens near thetip of the endoscope. The outflow port is connectable with an outflowtube which transports the waste fluid from the cavity to a suitablewaste fluid collecting reservoir. A set of fiber optic bundles containedinside the telescope transmit light energy produced by an external lightsource. This light energy illuminates the walls of the tissue cavity.The image thus formed is carried via a separate set of optical pathwaysagain situated inside the telescope. A video camera attached to the eyepiece of the telescope forms a clear endoscopic image of the cavity on aTV monitor. The endoscopic surgeon has to continuously look at the TVmonitor all through the endoscopic procedure.

Basic Layout of a ‘Continuous Flow Irrigation System:

Henceforth in this manuscript unless otherwise specified the term‘distension’ shall be deemed to imply tissue cavity distension by‘continuous flow irrigation’ only and the term ‘cavity’ unlessspecifically stated shall be deemed to refer to a ‘body tissue cavity’.In a typical distension system a physiological non viscous liquid like0.9% normal saline, 1.5% glycine, mannitol, ringer's lactate and 5%dextrose is stored in a sterile fluid source reservoir. A fluid supplytube connects the said fluid reservoir with the inlet end of a pump. Theoutlet end of the inflow pump is connected to the inflow port of anendoscope. When the inflow pump operates the fluid from the fluid sourcereservoir is sucked via the fluid supply tube and the inflow pump pushesthis fluid into the tissue cavity via the said inflow tube. The pumpoperates by consuming certain amount of energy and as a result of this apositive fluid pressure is created inside the tissue cavity. An outflowtube extends between the outflow port and the inlet end of an outflowpump. When the outflow pump operates it actively extracts waste fluidfrom the cavity again at the expense of energy and this waste fluid isultimately sent to a waste fluid reservoir via a tube which connects theoutlet end of the outflow pump with the waste fluid reservoir.Alternatively the outflow pump may be missing and in such case theoutflow tube directly carries the waste fluid from the cavity to thewaste fluid reservoir and the energy for such act is supplied by gravityinstead of the outflow pump. Also, the inflow pump may be missing and insuch case the inflow tube directly supplies the irrigation fluid from afluid source reservoir to the cavity. In such case the fluid sourcereservoir is hung at a suitable height above the patient and the saidenergy for cavity distension is derived from gravity instead of theinflow pump. A suitable pressure transducer is attached to the inflowtube, the outflow tube or directly to the cavity to measure the fluidpressure. A controller may be incorporated to regulate the system.

The Simplest Continuous Flow Irrigation System:

In its simplest form, a continuous flow irrigation system comprises afluid reservoir bottle hung at a suitable height above the patient andan inflow tube connecting this fluid reservoir to a tissue cavity. Anout flow tube is incorporated to remove fluid from the tissue cavity. Inthis system there is no pump and no transducer. In such a system fluidflows from the fluid source reservoir into the cavity and the requiredenergy is supplied by gravity. The pressure developed inside the cavitycan be increased or decreased by elevating or lowering the height of thefluid source reservoir. In such system the main limiting factor is theheight of the room ceiling beyond which the fluid reservoir cannot beraised. This is a crude system having negligible practical importanceand has been included only from the academic point of view. Also in sucha system unlimited volume of irrigation fluid may enter into thepatient's blood circulation. Thus such system is not suitable even fromthe patient safety point of view.

Basic Components of a Continuous Flow Irrigation System:

Like a motor car is made up of certain obvious components like engine,tyres and a steering wheel, a continuous flow distending system is madeof components like pump, pressure transducer, flow regulating valve,rubber tubes and a controller. The pump may be a positive displacementpump like a peristaltic pump, piston pump or a gear pump oralternatively it may be a dynamic pump like a centrifugal pump. Furtherthe said pump may be of a fixed RPM type which runs at fixed RPM allthrough the endoscopic procedure or the pump may be of a variable RPMtype which operates at variable RPM during the endoscopic procedure. Itis extremely important to note that fixed RPM pumps and variable RPMpumps are two separate mechanical entities in context with a cavitydistending system because the fixed and variable RPM pumps impartdifferent surgical efficiency and patient safety criteria to thedistending system. The said pump may be attached on the inflow sideonly, on the outflow side only or both on the inflow and outflow side.Further if a pump is attached only on the inflow side the outflow tubemay directly empty in a waste fluid reservoir at atmospheric pressure ora vacuum source may also be additionally attached. In some distendingsystems a flow controlling valve is attached on the outflow tube inorder to regulate the cavity pressure. There may be a single pressuretransducer attached to the inflow tube, the outflow tube or directly tothe cavity. In some systems instead of one pressure transducer twopressure transducers may be used, one on the inflow tube and the otheron the outflow tube.

Relvant references have been included in a PCT application filed by theInventors in the past numbered PCT/IB/002341 and the same may also bedeemed to have been included in the present application. In addition,three references U.S. Pat. Nos. 5,520,638, 4,902,277 and 5,578,012 arenow being included and discussed herebelow.

In the U.S. Pat. No. 5,520,638 a variable speed peristaltic pump is usedto push irrigation fluid into a tissue cavity. This patent is related tothe ‘Continuous Wave II Arthroscopy Pump’ marketed by Arthrex. A chamberwith volume is connected to the inflow tube and a collapsible bladder iscontained within the bladder. The collapsible bladder has an open endconnected with tubing to a pressure transducer. Once activated the pumpbegins to introduce fluid into the tissue cavity via the inflow tube andas pressure builds within the tissue cavity, fluid enters the chamber,and air in the chamber is compressed. The compressed air in the chambercompresses the bladder. Air pressure in the bladder is experienced bythe pressure transducer. The pressure transducer feeds pressureinformation to a controller which regulates the RPM of the pump on thebasis of a pressure feedback mechanism. Thus by the help of a pressurefeedback mechanism the pressure inside a tissue cavity is maintained byfluctuating around a desired value. In this invention an importantpurpose of the said chamber is to dampen the pressure pulsations createdby the peristaltic pump. Such pressure pulsations create turbulenceinside the tissues cavity and are hence undesirable. The method ofdampening the pressure pulsations as described in this U.S. Pat. No.5,520,638 is not adequately efficient, especially at high pump RPM's.The Inventors would like to submit that the system being claimed in theaforesaid US Patent is a passive dampening system. The system is onlyable to passively correct the small pressure pulsations. In the presentinvention a method shall be described by which the amplitude of the saidpressure pulsations would be reduced to negligible magnitude even at ahigh pump RPM.

In U.S. Pat. No. 4,902,277 a pump is provided on the inflow side whichpushes fluid into a tissue cavity while a positive displacement pumpremoves fluid from the cavity. This patent is related to ‘FMS duo FluidManagement System’ marketed by FMS Group. By the help of a pressurefeedback mechanism the inflow pump is constantly increased or decreasedthereby maintaining the cavity around a desired value. Thus by the helpof a pressure feedback mechanism the pressure inside a tissue cavity ismaintained by fluctuating around a desired value.

In U.S. Pat. No. 5,578,012 a centrifugal pump is deployed on the inflowside while no pump is deployed over the outflow side. This patent isrelated to the ‘HydroFlex HD’ pump marketed by DAVOL company. By thehelp of a pressure feedback mechanism the inflow pump is constantlyincreased or decreased thereby maintaining the cavity around a desiredvalue. Thus by the help of a pressure feedback mechanism the pressureinside a tissue cavity is maintained by fluctuating around a desiredvalue.

OBJECTS OF THE INVENTION

The overall objective of the invention is to provide a safe, efficientand turbulence free system for distending body tissue cavities for thoseendoscopic procedures which utilize continuous flow irrigation.

The main object of the invention is to minimize the amplitude as well asthe frequency of pressure pulsations, inside the tissue cavity, createdby the two positive displacement pumps.

Another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to create andmaintain a desired precise cavity pressure for a desired precise rate atwhich fluid may be allowed to flow through the cavity, for any length oftime.

Still another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to achieve apredictably constant clear endoscopic vision throughout the endoscopicprocedure.

Yet another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to achievepredictably stable mechanical cavity distension throughout theendoscopic procedure.

One more object of the present invention is to provide a system fordistending tissue cavities using which it being possible to predictablymaintain the cavity pressure at any desired precise value despitephysiological contractions of the cavity wall.

One another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to constantly,accurately and reliably determine the instantaneous real time rate offluid intravasation into the patient's body by using two fluid flow ratesensors which do not have any movable components.

A further more object of the present invention is to provide a systemfor distending tissue cavities using which it being possible to maintainany desired precise and high cavity pressure without increasing the‘maximum possible fluid intravasation rate’.

Another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to measure theactual cavity pressure, in an accurate, reliable and simple manner, byusing a pressure transducer located far away from the cavity in the upstream portion of the inflow tube.

Yet another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to make thepressure inside the body cavity and the flow rate of the fluid passingthrough the body cavity absolutely independent of each other such thatthe value of any may be altered without affecting the value of theother.

Still another object of the present invention is to provide a system fordistending tissue cavities using which it being possible to reduce thecavity filling time in a predictably controlled manner and at the sametime achieving a desired cavity pressure at the end of the cavityrefilling phase, cavity refilling time being the time taken tocompletely fill a cavity with the irrigation fluid.

One more object of the present invention is to provide a system fordistending tissue cavities using which it being possible for the surgeonto have a fairly accurate assessment of the total volume of theirrigation fluid which would be required to complete the entireendoscopic procedure.

One another object of the present invention is to provide a system fordistending tissue cavities using which it being possible for the surgeonto accurately know the maximum pressure which develop inside the cavityin case of an accidental obstruction of the outflow tube and it shouldbe possible to minimize such rise in the cavity pressure in a controlledand predictable manner.

A further object of the present invention is to provide a system fordistending tissue cavities using which it being possible to easily,quickly and safely change from one type of irrigation fluid to adifferent type of irrigation fluid, for example between normal salineand glycine, intraoperatively (that is during a surgical procedure), inany desired short period of time such that the cavity pressure does notchange during such maneuver.

SUMMARY OF THE INVENTION

The present invention provides a safe and an efficient system fordistending body tissue cavities for those endoscopic procedures whichutilize continuous flow irrigation. The main aim of the invention is tominimize cavity fluid turbulence by minimizing the amplitude as well asthe frequency of the pressure pulsations created by two positivedisplacement pumps. The present invention is a system of creating andmaintaining a desired positive pressure inside a body tissue cavitythrough which fluid is made to flow at a desired flow rate.Alternatively the present invention may be considered as a system ofcreating cavity fluid pressure which is absolutely independent of thecavity outflow rate. The present invention comprises of two peristalticpumps which work simultaneously, for indefinite time, at fixed flowrates to create and maintain any precise desired cavity pressure for anydesired cavity outflow rate, including a zero outflow rate. One pump islocated on the inflow side of a cavity while the other pump is attachedto the out flow side of the cavity. Further if any fluid is beingabsorbed into or through the cavity walls, such as fluid intravasationwhich occurs during hysteroscopic endometrial resection, theinstantaneous real time rate of such fluid absorption can be constantlydetermined. Also the cavity pressure can be maintained at any desiredhigh value without increasing the ‘maximum possible fluid intravasationrate’. In the proposed invention by incorporating a system of pumpsynchronization it is possible to reduce fluid turbulence to almostnegligible levels. The proposed invention also has multiple otherfeatures of endoscopic surgical relevance which greatly enhance thepatient safety and efficiency during endoscopic surgery few suchfeatures being shortening of the cavity refilling time in a predictablycontrolled fashion, to be able to predict by a fair degree of accuracythe volume of fluid which would be required to complete the endoscopicprocedure, to be able to quickly switch during endoscopic surgerybetween two types of irrigation fluids without varying the cavitypressure and to be able to predict and limit the magnitude of themaximum increase in the cavity pressure or the magnitude of a minorpressure surge which might occur in case of an accidental obstruction ofthe outflow tube for a specific outflow rate. Also the same system canbe used for all types of endoscopic procedures which utilize continuousflow irrigation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the main block diagram of the invention along with the‘pressure pulse dampening system’ and the controller.

FIG. 2 shows the block diagram of the invention without the ‘pressurepulse dampening system’.

FIG. 3 is similar to FIG. 2 except that the controller has not beenincluded.

FIG. 4 shows the inflow part of the system along with the inflowperistaltic pump 5, the pressure transducer 17 and the constriction site8.

FIG. 5 is similar to FIG. 3 except that in this figure a shaded regionrepresents an area having an almost similar pressure.

FIG. 6 is similar to FIG. 3 except that an optional constriction housingtube 17 and an optional pressure transducer 63 have been included.

FIG. 7 shows is the schematic diagram for pump synchronization on acommon rotor shaft.

FIG. 8 shows the basic lay out of the ‘pressure pulse dampening system’.

FIG. 9 shows a detailed layout of the syringe mechanism along with acoupling means.

DETAILED DESCRIPTION OF INVENTION

Accordingly, the present invention provides a system for distending bodytissue cavities of subjects by continuous flow irrigation duringendoscopic procedures the said system comprising:

a fluid source reservoir containing a non viscous physiologic fluidmeant for cavity distension;

a fluid supply conduit tube connecting the fluid source reservoir to aninlet end of a variable speed positive displacement inflow pump and anoutlet end of the said inflow pump being connectable to an inflow portof an endoscope instrument through an inflow tube for pumping the fluidat a controlled flow rate into the cavity, the flow rate at which thefluid enters into the cavity via the inflow tube being termed as thecavity inflow rate;

an inflow pressure transducer being located anywhere in the inflow tubebetween the outlet end of the inflow pump and the inflow port of theendoscope;

an inflow pressure pulsation dampening means connected to the inflowtube for dampening the pressure pulsations inside the cavity created bythe positive displacement inflow pump,

an outflow port of the endoscope being connectable to an inlet end of avariable speed positive displacement outflow pump through an outflowtube for removing the fluid from the cavity at a controlled flow rate,the flow rate of the said outflow pump being termed as the cavityoutflow rate,

an outflow pressure pulsation dampening means connected to the outflowtube for dampening the pressure pulsations inside the cavity created bythe positive displacement outflow pump;

an outlet end of the outflow pump being connected to a waste fluidcollecting container, and

a housing tube having a controllable constriction site is being providedbetween the fluid source reservoir and the inflow tube such that thesame by-passes the inflow pump; wherein housing tube provides a routefor any excess fluid being pumped by the inflow pump to bypass theinflow pump and go back to the fluid supply tube or the fluid sourcereservoir, thereby minimizing turbulence inside the cavity andmaintaining the cavity pressure at a stable value despite physiologicalcontractions of the cavity wall.

In an embodiment of the present invention, the fluid source reservoircontaining the non-viscous physiologic fluid is maintained atatmospheric pressure or at a pressure greater than the atmosphericpressure.

In another embodiment of the present invention, a proximal open end ofthe fluid supply tube is connected to the fluid source reservoir and adistal end of the tube is connected to the inlet end of the variablespeed positive displacement inflow pump.

In yet another embodiment of the present invention, the proximal openend of the fluid supply tube is constantly and completely immersed inthe fluid source reservoir.

In still another embodiment of the present invention, a proximal end ofthe inflow tube is connected to the outlet end of the variable speedpositive displacement inflow pump and a distal end of the inflow tubebeing connectable to the inflow port of the endoscope instrument.

In a further embodiment of the present invention, the variable speedpositive displacement inflow pump is selected from the group comprisingperistaltic pump, piston pump, gear pump, diaphragm pump and plungerpump.

In one more embodiment of the present invention, the variable speedpositive displacement inflow pump is a peristaltic pump.

In one another embodiment of the present invention, the housing tube isreleasably provided between the fluid source reservoir and the inflowtube to enable replacement of the housing tube with yet another housingtube having a different diameter at the constriction site to suit theoperational need of the endoscopic procedure.

In one further embodiment of the present invention, a proximal end ofthe housing tube is connected to the fluid supply tube near its distalend close to the inlet port of the inflow pump.

In a further more embodiment of the present invention, a proximal end ofthe housing tube empties directly into the fluid source reservoir and isconstantly and completely immersed in the fluid source reservoir.

In an embodiment of the present invention, a distal end of the housingtube is connected to the inflow tube near its proximal end close to theoutlet end of the inflow pump.

In another embodiment of the present invention, the housing tube isprovided with a clamping means at the constriction site to enable theuser to vary the diameter of the housing tube at the constriction siteto suit the operational needs of endoscopic procedures.

In yet another embodiment of the present invention, the diameter of thehousing tube at the constriction site is in the range of 0.001 mm to amaximum value which is less than the overall diameter of the rest of thehousing tube.

In still another embodiment of the present invention, the diameter ofthe housing tube at the constriction site is in the range of 0.01 to 2.5mm.

In one more embodiment of the present invention, the inflow pressuretransducer is located sufficiently away from the cavity site, preferablynear the outlet end of the inflow pump from the practical point of view,such that the fluid pressure measured by the same is almost equal to thefluid pressure inside the cavity.

In a further embodiment of the present invention, a proximal end of theoutflow tube being connectable to the outlet port of the endoscopeinstrument and a distal end of the outflow tube is connected to an inletend of the variable speed positive displacement outflow pump.

In one another embodiment, the present invention further comprising anoutflow pressure transducer connected between the proximal end of theoutflow tube and the inlet end of the variable speed positivedisplacement outflow pump for measuring the pressure in the outflowtube.

In one further embodiment of the present invention, the variable speedpositive displacement outflow pump is selected from the group comprisingperistaltic pump, piston pump, gear pump, diaphragm pump and plungerpump.

In an embodiment of the present invention, the variable speed positivedisplacement outflow pump is a peristaltic pump.

In another embodiment of the present invention, the outlet end of thevariable speed positive displacement outflow pump is connected to thewaste fluid collecting container through a waste fluid carrying tube.

In yet another embodiment, the device of the present invention furthercomprising a micro-controller means electrically coupled to the inflowpressure transducer, the outflow pressure transducer, the inflow pumpand the outflow pump for regulating the operation of the inflow and theoutflow pumps.

In still another embodiment, the device of the present invention furthercomprising a housing tube having a variable size constriction site beingprovided between the outflow tube and the waste fluid reservoir.

In a further embodiment of the present invention, the distal end of thehousing tube is connected to the waste fluid carrying tube.

In one more embodiment of the present invention, the fluid supply tube,the inflow tube, the outflow tube and the waste fluid carrying tube areflexible, disposable and are made of polymeric material.

In one another embodiment of the present invention, the inflow and theoutflow positive displacement pumps are coupled to a common shaft forsynchronously operating these two pumps.

In one further embodiment of the present invention, the inflow housingtube is provided with an electromechanical device, a solenoid, to enablethe micro-controller to vary the diameter of the constriction site.

In an embodiment of the present invention, wherein if the inflow and theoutflow pumps are coupled to the common shaft, the inflow housing tubeis essentially provided with the micro-controller controlled solenoidfor varying the diameter of the constriction site.

In another embodiment of the present invention, the variable speedinflow and outflow peristaltic pumps are provided with 1 to 5peristaltic pump tubes connected in parallel between the inflow andoutflow ends of the peristaltic pumps for reducing the frequency ofpulsations in the pressure, the said tubes being connected to each otherat the inflow and outflow ends of the peristaltic pumps, and the saidperistaltic pump tubes being the ones which come in contact with therollers of the peristaltic pumps.

In yet another embodiment of the present invention, the inflow pressurepulsation dampening means comprises a single outlet syringe mechanism,the piston of the same being coupled synchronously to the positivedisplacement inflow pump through a coupling means and a single outletend of the said syringe mechanism being connected to the inflow tube.

In still another embodiment of the present invention, the outflowpressure variation dampening means comprises a single outlet syringemechanism, the piston of the same being coupled synchronously to thepositive displacement inflow pump through a coupling means and a singleoutlet end of the said syringe mechanism being connected to the outflowtube.

In one more embodiment of the present invention, if the inflow and theoutflow pumps are operated synchronously by coupling them to the commonshaft, the inflow and/or the outflow pressure variation dampening meansare optionally operated synchronously by coupling them to the samecommon shaft.

In one another embodiment of the present invention, a fluid flow ratesensor is located in the lumen or wall of the fluid inflow tube formeasuring the cavity inflow rate.

In yet another embodiment of the present invention, the fluid flow ratesensor is located between the inflow port of the endoscope and thelocation where the housing tube is connected to the fluid inflow tube.

In still another embodiment, the device of the present invention furthercomprises a fluid flow rate sensor connected between the proximal end ofthe outflow tube and the inlet port of the variable speed positivedisplacement outflow pump for measuring the cavity outflow rate.

In one more embodiment of the present invention, the fluid flow ratesensor is located between the outflow port of the endoscope and a placeproximal to the point where the said additional/optional housing tube isconnected to the outflow tube.

In one another embodiment of the present invention, the fluid flow ratesensors consists of a heating coil in physical contact with a metalplate for heating the same and a temperature sensor placed in contactwith the metal plate for measuring the temperature of the said metalplate, the temperature of the metal plate being a function of the fluidflow rate.

In a further embodiment of the present invention, the fluid flow ratesensor is a hot wire anemometer.

In a further embodiment of the present invention, instantaneous realtime rate of fluid intravasation is determined by electricallyconnecting the inflow and outflow fluid flow rate sensors to amicro-controller.

In a further more embodiment of the present invention, the fluid sourcereservoir, the inflow pump, the tubes, the tissue cavity, and the outflow pump are placed approximately at the same height with respect to ahorizontal ground.

In another embodiment of the invention the two positive displacementpumps, which may be peristaltic pumps, are attached on a common singlecentral shaft such that a single motor operates both pumpssimultaneously and such arrangement being provided as it further reducesfluid turbulence inside the tissue cavity.

The proposed invention is described hereafter with reference to theaccompanying drawings in order to clearly explain and illustrate thesystem and the working of the system. It is respectfully submitted thescope of the invention should not be limited by the description beingprovided hereafter.

The system of the present invention is a unique system for distendingbody tissue cavities in endoscopic procedures. In the proposed inventiona body tissue cavity is distended by continuous flow irrigation in sucha manner that the amplitude of the pressure pulsations created by thepositive displacement pumps can be reduced to a negligible value. In theproposed invention a method of reducing of the said pulsations has beendescribed. Also the cavity pressure is absolutely independent of thecavity outflow rate, such the both, the cavity pressure and the outflowrate, may be independently altered without varying the value of theother parameter.

FIG. 1 shows the main diagram of the invention. In FIG. 1 the inflow andthe outflow ‘pressure pulse dampening systems’, have been shown clearly.However in order understand the invention in a simpler manner, first thebasic invention without the ‘pressure pulse dampening systems’ shall bediscussed. The basic schematic diagram of the invention is shown in FIG.2. FIG. 2 is similar to FIG. 1 except that in FIG. 2 the two ‘pressurepulse dampening systems’ have not been included. The two peristalticpumps 5 and 14 operate simultaneously in order to distend a tissuecavity in such a manner that the cavity pressure is totally independentof the cavity outflow rate. FIG. 2 represents the complete basicschematic diagram of the invention. Please note that the controllerbeing used in the system shown in FIG. 2 is an optional feature and thesystem would provide most of the features even without the controller.The FIG. 3 represents the schematic diagram of the invention but withouta controller system. Thus FIG. 3 is a basic mechanical version of theinvention. A human operator is required to operate such mechanicalversion of the invention shown in FIG. 3. Though it is recommended thatthe controller based version of the invention be used in endoscopicsurgeries, it is not essential. The controller being used in the presentinvention merely assists the user in arriving easily at some of theadditional functions which otherwise can be performed manually. Thus, inthis manuscript the mechanical version of the invention shown in FIG. 3is being discussed in more detail in order to explain the basic physicalprincipals of the invention with a greater clarity.

Referring to FIG. 3, the system shown in this figure comprises of twoperistaltic pumps which can maintain a predictably precise stable cavitypressure for indefinite time by working simultaneously at constantrotational speeds. Pump 5 pushes fluid into the cavity 18 and while pump14 simultaneously extracts fluid out of the cavity 18. The inlet end ofthe inflow peristaltic pump 5 is connected to a fluid source reservoir 1via tube 2. The distal open end of tube 2 is constantly submerged in asterile non viscous physiological fluid like 0.9% normal saline, 1.5%glycine, ringer lactate or 5% dextrose contained inside the reservoir 1at atmospheric pressure. One end of the tube 7 connects the ‘T junction’3 situated at the inlet end of the pump 5 while the other end of tube 7connects with the ‘square junction’ 6 situated at the outlet end of thepump 5. The ‘T’ junction 3 is thus the meeting point of three tubes,namely 2, 4 and 7. Similarly the square junction 6 is the meeting pointof four tubes, 4, 9, 7 and 10. The rollers of the peristaltic pump 5continuously compress and roll over the entire length of tube 4 thusdisplacing fluid in the direction of the curved arrow. This curved arrowdenotes the direction in which the rollers of the peristaltic pump 5rotate. Tube 7 has a constriction point 8 which can be located anywherealong its length. Such constriction point refers to a point where theinner diameter of the lumen of tube 7 is reduced in comparison to thelumen of the rest of the tube 7. Such constriction may be a permanentconstriction in the lumen of tube 7 or it may be a variable constrictionwhose diameter may be increased or decreased as desired. A pressuretransducer 17 is attached at one of tube 9 while the other end of tube 9is connected anywhere on inflow tube 10. For practical convenience it isdesirable that the said other end of tube 9 be connected in the upstream part of the inflow tube 10 such as at the square junction 6. Thepressure transducer 17 measures the fluid pressure via a column ofliquid or air present in the lumen of tube 9. The fluid pressure asmeasured by the pressure transducer shall be referred to as P. In thismanuscript the term ‘P’ shall frequently be used to refer to the actualpressure inside the tissue cavity but in physical terms P is thepressure sensed by the transducer 17 at point 6. The pressure transducer17 may also be in the form of a membrane diaphragm incorporated in thewall of the inflow tube 10 such that this membrane diaphragm is indirect contact with the fluid contained in the inflow tube 10, such thatthe linear movement excursions of the said membrane are, interpreted aspressure of the fluid inside the inflow tube 10 by a suitable pressuretransducer. Such type of pressure sensor being directly incorporated inthe wall of the inflow tube 10 senses the fluid pressure without theintervention of tube 9. The basic purpose of the transducer is tomeasure the fluid pressure inside the inflow tube 10, such as at point6, thus the mechanical construction of the transducer is not importantas long as it measures the fluid pressure. For the sake of simplicitythe existence of tube 9 shall be continued to be considered in the restof the manuscript. The peristaltic pump 14 attached to the outflow sideactively extracts fluid out of the tissue cavity 18 via the out flowtube 12. The outlet end of the pump 14 is connected to a waste fluidcarrying tube 15 which opens into a waste fluid collecting reservoir 16at atmospheric pressure. The rollers of the pump 14 constantly compressand roll over the entire length of the peristaltic pump tubing 13 thusdisplacing fluid in the direction of the curved arrow which alsocorresponds with the direction of pump rotation.

In order to understand the invention in a simpler manner both pumps arebeing considered to be identical in all respects and all the tubes, theinflow and out flow port are also being considered to be having the sameuniform inner diameter. However the inner diameter of the tubes and theinflow and outflow ports can also be different. The inflow and outflowports are metallic adaptors located at the proximal end of the endoscopeand are meant to connect with the inflow and outflow tubes respectively,however the said inflow and outflow ports have not been separately shownin any of the figures. Tubes 4 and 13 consist of a soft resilientplastic material which can be efficiently compressed by the rollers ofthe peristaltic pumps. The other tubes also consist of a suitableresilient plastic material. It is assumed that all the components shownin FIG. 3, including the two pumps, all tubes and the said cavity, areplaced at the same horizontal height with respect to the ground. Alsothe rollers of pumps 5 and 14 should press adequately over tubes 4 and13 in such a manner that there is no leak through these tubes when thepumps are stationary. It is also assumed that there is no abnormal leakof fluid in the irrigation system, for example leak via a accidentalhole made in any irrigation tube or a fluid leak which might occur ifthe endoscope loosely enters into the tissue cavity, for example inhysteroscopic surgery fluid leaks by the sides of the endoscope if thecervix is over dilated.

One end of the constriction site housing tube 7 instead of beingconnected with tube 2 at the ‘T’ junction 3 can also open directly intothe fluid source reservoir 1. This shall not affect the efficiency ofthe system in any way but it may be practically difficult from thesurgical point of view in some special cases. Thus such a provision isseparately shown in FIG. 6 and the said tube has been labeled as 11 butit has intentionally not been included in FIGS. 1,2 and 3 in order tokeep the drawings simple. Also a constriction site housing tube similarto tube 7 labeled as 17 can be attached to the outflow tube 12 as shownin FIG. 6. In the said tube 17 the said constriction site is labeled as19. Such tube can serve a number of purposes. Tube 17 can be utilizedfor relatively faster evacuation of air bubbles from the cavity. Thesaid bubbles are invariably created inside the cavity as a result ofelectrosurgical cutting and coagulation or they may enter the cavitywhile the endoscope is being introduced into the cavity. Such bubblescause extreme nuisance for the surgeon because they obscure vision andthus the surgical time may be greatly increased. In routine surgery thesurgeon moves the tip of the resectoscope near the bubble and the bubbleis sucked out of the cavity by the process of continuous flowirrigation. However in certain situations it may not be possible tobring the tip of the resectoscope near the bubble, one such situation iswhen bubbles accumulate inside a very deep cornuae associated with along septum, the diameter of the cornuae being less than the outerdiameter of the resectoscope. In such a situation the tubal openingsituated at the center of the cornuae can only be visualized afterevacuating such bubbles from the cavity. In such situation the bubblescan be quickly evacuated without moving the tip of the resectoscope nearthe bubbles by simply opening the constriction 19 in the tube 17.However such maneuver tends to completely collapse the cavity. Thus ifthe resctoscope tip is only moderately away from the bubbles theconstriction is opened only partially so that the bubbles are sucked outand the cavity collapses by a relatively smaller magnitude. In place ofthe adjustable constriction site 19 a pressure release safety valve maybe incorporated as a safety feature, however it is more beneficial toinstall such pressure safety valve in the inflow circuit. The tube 17may also be used for quickly flushing air bubbles from the irrigationtubes by fully opening the constriction site 19 for a few minutes orseconds. The tube 17 may also be used for any other purpose as deemedfit by the surgeon. However the said tube 17 has intentionally not beenincluded in the main block diagrams of the invention because byincluding the tube 17 in the main block diagrams it would have becomevery difficult to explain the basic physical principals of theinvention. However tube 17 is a very beneficial component and is thusrecommended to be incorporated in the system of the proposed invention.The opening and closing of the constriction site 19 can also beregulated manually to help in various special advanced endoscopicapplications. Incorporation of tube 17 with the variable constrictionsite 19 can help in reducing the substantially high amplitude pressurevariations inside the cavity caused by abnormally large cavity wallcontractions, but such phenomenon is only rarely encountered. Also anadditional pressure transducer 63 may also be attached on the out flowtube 12, if desired, as shown in FIG. 6. However the said pressuretransducer 63 has intentionally not been included in the main blockdiagrams of the invention because by doing so it would have become verydifficult to explain the basic physical principals of the invention.

In order to clearly understand the system shown in FIG. 3 it would behelpful to discuss the functioning of the inflow peristaltic pump 5 as aseparate entity as shown in FIG. 4. The rollers of pump 5 move in thedirection of the curved arrow and squeeze over the entire length ofperistaltic pump tubing 4. Initially tubes 2, 4, 7 and 9 contain air atatmospheric pressure and the free open end of tube 2 is submerged in asterile fluid contained inside the fluid source reservoir 1. The momentthe constriction site 8 is fully occluded a column of fluid isimmediately sucked into tube 4 via tube 2, and thus fluid startsaccumulating in the proximal parts of tubes 9 and 7. As the fluid fillsin tube 9 it pushes a column of air distal to the fluid column createdin tube 9 and the pressure of this compressed air column is sensed bythe pressure transducer 17. The fluid pressure and the pressure of thesaid compressed air column are same thus the pressure transducer 17actually senses the fluid pressure. If tube 7 continues to remain fullyoccluded at the constriction site 8, the fluid continues to accumulateinside tubes 9 and in that part of tube 7 which lies between point 6 andthe constriction site 8, and the pressure transducer 17 thus displays acontinuously rising fluid pressure. The moment the block at theconstriction site 8 is partially released the fluid escapes in the formof a jet through the partially open constriction opening 8 in thedirection of point 3. With the constriction opening 8 being onlypartially blocked, if the pump 5 continues to rotate at a constantrotational speed the fluid pressure ultimately gets stabilized at afixed value provided the internal diameter of the constriction site 8 isnot further varied. The diameter D of the constriction site 8 rangesfrom a minimum non-zero value to a maximum value which is less than theoverall diameter of the rest of the housing tube, that is range betweenwhen the constriction site 8 is fully occluded, to a maximum value whichis less than the diameter of tube 7. Henceforth in this manuscript theinner diameter of the constriction site 8 shall be deemed to be fixed atsome predetermined value D, unless otherwise stated.

Referring to FIG. 5, this figure is similar to FIG. 3 but a limitedregion of the irrigation circuit having an almost same pressure has beenshaded black. Due to frictional resistance experienced by the movingfluid the pressure at point 6, as sensed by the transducer 17, is alwaysfound to be higher than the actual pressure inside the tissue cavity 18but the said pressure difference is so small that it may be neglectedfrom the practical surgical point of view. Also such pressure differenceincreases as the fluid flow rate increases. In a simulated experimentalendoscopic model, as explained hereafter, such pressure difference wasfound to be only 2 mm Hg at a out flow rate of 500 ml/minute, while atoutflow rates less than 400 ml/minute this pressure difference was sosmall that it had not been possible to demonstrate it experimentally.The term ‘out flow rate’ being referred to the flow rate of pump 14.Also, the said pressure difference remains constant all through surgeryat any fixed outflow rate. Though the said pressure difference isnegligible but if desired its effect can also be totally negated bysubtracting its value from the pressure reading of the transducer. Inthis manner, in endoscopic surgeries, it is possible to determine theactual cavity pressure by using the pressure transducer 17 located faraway from the cavity. This feature is of special relevance because inendoscopic procedures like hysteroscopy, arthroscopy and brainendoscopic surgery while it is important to know the actual cavitypressure but at the same time it is practically difficult to take apressure measurement directly from the cavity.

Referring to FIG. 3 it shall be first described as to how the system ofthe proposed invention can be used mechanically, that is without acontroller. The peristaltic pumps 5 and 14 can be made to work at anyfixed rotational speed and the fluid flow rate of each pump is directlyproportional to the pump RPM or the pump rotational speed. Thus anyprecise pump flow rate can be generated by selecting a suitable pumprotational speed. The fluid flow rate of pump 14 shall henceforth bedenoted by R2 and shall be termed as the ‘outflow rate’. The fluid flowrate of pump 5 shall be denoted by R1 and shall be termed as the ‘inflowrate’ Here it is to be noted that the term ‘inflow rate’ R1 is not thetrue inflow rate for the cavity 18, as might be suggested by theliterary meaning of the term ‘inflow’ because R1 is not the actual rateat which fluid into the cavity 18 because some fluid also constantlyescapes through the constriction site opening 8. Henceforth in theentire manuscript the term ‘inflow rate’ shall only be referred to theflow rate of the inflow pump 5 unless specifically mentioned. Howeverthe term ‘outflow rate’ R2 does correspond to the literary meaning ofthe term ‘outflow’ because R2 is equal to the rate at which fluid flowsout of the cavity 18. The surgeon initially decides an out flow rate R2by selecting a suitable rotational speed for pump 14. Next the surgeondecides the maximum flow rate at which fluid could be allowed to enterinto the cavity via the inflow tube 10 and the inflow pump 5 is set towork at such flow rate or at a flow rate slightly lesser than this. Asalready discussed, intravasation is process by which fluid enters intothe patient's blood circulation through the cut ends of blood vesselslocated in the cavity wall or enters into the patient's body, forexample into the peritoneal cavity, as a result of an accidentalperforation or escapes via patent fallopian tubes into the peritonealcavity. Thus ‘intravasation’ is a process by which the pressurizedirrigation fluid enters into the patient's body system through the wallsof the tissue cavity. In case of a surgical accident like cavity wallperforation the fluid being pumped by the inflow pump 5 can enter intothe patient's body at a rate almost equal to R1. It is obvious that themaximum rate of fluid intravasation cannot exceed the value R1. In caseof an accident like cavity wall perforation it may take some time beforean abnormally high intravasation rate is discovered and in such time adangerous quantity of fluid might enter into the patient's body. If theinflow rate R1 is kept at a relatively lower value then the volume ofintravasated fluid in case of such an accident would be low. Afterfixing the values for R2 and R1 the system is started and the diameterof the constriction site 8 is gradually reduced. As the diameter of theconstriction site 8 is reduced fluid starts flowing into the tissuecavity and the pressure inside the tissue cavity starts rising. When thedesired pressure is achieved inside the tissue cavity the diameter ofthe constriction site 8 is not reduced any further and is fixed. Thediameter of the constrictions site at this stage is termed as “D”. Theconstriction site may also be a plastic or metal piece which has a holein the centre such that the diameter of the hole is permanently fixed atsome value D. If a constriction 8 has a permanently fixed diameter thenonly the flow rates of pumps 14 and 5 have to be set before the systembecomes completely operational.

The Inventors here would like to discuss about the importance ofincorporating the housing tube 7 with the constriction site and thenon-obvious advantages provided by the housing tube 7 with theconstriction site.

As mentioned earlier, till date the surgeons were left with only twooptions, either to ignore the said cavity pressure variations by notcorrecting them, or to externally and actively correct such pressurevariations. To externally and actively correct the variations in thecavity pressure, controller was incorporated and the working of thepumps were essentially controlled by the controller. Incorporation ofthe controller controlling the operation of the pumps did not provideany benefit. The controllers used to activate the controlling actionafter the variations in the cavity pressure had subdued. Thus, thecontrolling action initiated by the controller instead of benefiting thesurgeon leads to an undesirable turbulence inside the cavity and alsotends to amplify the resultant movement excursions of the cavity walls.

The Inventors have noticed that if the controller continuously controlsthe operations of the pumps (either on the inflow side or on the outflowside), the cavity pressure continuously fluctuates around a preset valueand it not at all possible to attain a constant value. The Inventorsbelieve that the controller provides proper corrective action (bycontinuously controlling the operations of the pumps) only if thefluctuations in the cavity pressure are gradual and not highlyinstantaneous. That is, if the quantitative rise/fall in the cavitypressure is over long time period, the controller would be able toprovide proper corrective action. As the time period to detect variationin the cavity pressure and commence corrective action is ideally in therange of 2 to 4 seconds, if the quantitative rise/fall in the cavitypressure is over very short time period, the suggested mechanism ofproviding a controller will be unsuitable. Under such instances, insteadof providing any corrective action, the controller destabilizes thesystem and induces additional pressure fluctuations inside the cavity(because of commencing a corrective action at a delayed stage). Thus ittakes very long time period for the system to once again get stabilized.

The Inventors have surprisingly found that by incorporating a housingtube provided with a constriction site at the inflow side as describedabove, inherently and passively corrects the pressure variations due tophysiological cavity wall contractions and the mechanical movement ofthe tubes and the endoscope and also limits the variation in the size ofthe cavity. The Applicants would like to highlight that it is importantto control both the variations in the pressure inside the cavity and thechanges in the size of the distended cavity. Large variations in thepressure inside the cavity or the size of the cavity are detrimental tothe surgical procedure. In all the prior art systems attempts were madeto either control the variations in the pressure or the variations inthe cavity size. But none of the prior art document the need to controlboth the cavity pressure variations and the cavity size variations andhence failed to provide a safe and ideal system. During the contractionof the cavity, a minute quantity of the fluid is pushed out of thecavity. If during this stage the system does not provide a way forreleasing the fluid being pushed out, the instantaneous pressure insidethe cavity increases tremendously which is harmful to the patient. Onthe other hand, if the amount of fluid being pushed out of the cavity isnot checked and controlled, the changes in the size of the distendedcavity are very high. The incorporation of the housing tube having theconstriction site for the first time in the present system controls boththe variations in the pressure inside the cavity and the changes in thesize of the distended cavity. The housing tube having the constrictionssite provides a by-pass route for the fluid being pushed out of thecavity to go back to the fluid supply tube or the fluid sourcereservoir. This avoids the instantaneous pressure surge inside thecavity which is harmful to the patient. The size of the diameter at theconstriction automatically controls the amount of fluid passing throughthe housing tube, thereby controlling the amount of fluid being pushedout of the cavity. Inclusion of the housing tube with the constrictionsite therefore minimizes the instantaneous variations in the size of thedistended cavity.

Alternatively if the cavity expands a suitable volume of fluid is suckedinto the cavity from the irrigation circuit, such as from the region ofpoint 6, and this is accompanied by a corresponding transient decreasein the flow rate at which fluid which fluid is escaping via theconstriction site 8 in the direction of point 3 but if the magnitude ofthe said physiological expansion is more fluid may even be sucked intothe cavity via the constriction site 8. This implies that theconstriction site 8 is helping in maintaining a stable cavity pressuredespite physiological cavity wall contractions by suitably varying themagnitude of an imaginary fluid flow vector passing through theconstriction site 8.

Cavity Pressure or the Outflow Rate, Both can be Altered IndependentlyWithout Varying the Value of the Other Parameter:

Referring again to FIG. 3 an hypothetical endoscopic procedure is beingconsidered where surgery is being performed at an outflow rate R2 andinflow rate R1 with the constriction 8 diameter being been fixed at somevalue D and a resultant cavity pressure P being created maintained. Insuch hypothetical situation as long as R2 and R1 are not altered thecavity pressure P remains predictably constant throughout surgeryresulting in a predictably stable mechanical distension of the tissuecavity walls which culminates in constant clear visualization throughoutthe endoscopic procedure. If in the said hypothetical procedure thecavity pressure needs to be increased without altering the out flow rateR2 then all that is needed is to start increasing the value of R1 andstop doing so when the desired higher cavity pressure is achieved.Similarly if the cavity pressure needs to be decreased without alteringthe out flow rate R2 then R1 is decreased till the desired lower cavitypressure is attained. In the said hypothetical endoscopic procedure ifthe outflow rate R2 needs to be increased without altering the cavitypressure P then the value of R2 is increased by the desired magnitudebut simultaneously the value of R1 is also increased by a similarmagnitude. Similarly, if the outflow rate R2 needs to be decreasedwithout altering the cavity pressure P then the value of R2 is decreasedby the desired magnitude but simultaneously the value of R1 is alsodecreased by a similar magnitude. Thus if R1 and R2 are simultaneouslyincreased or decreased by the same magnitude the cavity pressure doesnot vary, the value D is always fixed as already stated. The precedingstatements shall now be explained by the help of a numericalhypothetical example. In reference to FIG. 3 considering a hypotheticalsituation in which an endoscopic procedure is being done at an outflowrate of 100 ml/minute, an inflow rate R1 and the cavity pressure being80 mm Hg. If the surgeon wants to increase the outflow rate to 322ml/minute by maintaining the cavity pressure at the same value of 80 mmHg outflow rate is increased to 322 ml/minute and the inflow rate isincreased by 222 ml/minute, because 322 ml/min−100 m/min=222 ml/minute.As already mentioned in this paragraph if both inflow and outflow ratesare increased or decreased by the same magnitude the cavity pressuredoes not change. Thus the final inflow rate becomes R1+222 ml/minute,where R1 was the initial inflow rate. Thus in the proposed invention thecavity pressure and the outflow rate both can be altered absolutelyindependent of each other without affecting the value of the otherparameter.

Mechanical Version of the Invention:

The mechanical version of the invention shown in FIG. 3 can be usedpractically in endoscopic surgeries but it requires a skilled operatorhaving a detailed knowledge of the physical principals involved incavity distension, which may not be always possible. Also the mechanicalversion has certain practical limitations which shall be explained inthe later sections of the manuscript. This mechanical version of theinvention has been discussed only in order to explain more clearly thephysical principals associated with the controller based version of thebasic invention shown in FIG. 2 and the main invention shown in FIG. 1.

Controller Based Version of the Invention:

Referring to FIG. 2, this figure shows a schematic diagram of the basicinvention without the ‘pressure pulse dampening system’. FIG. 2 and FIG.3 are similar except that in figure except that in FIG. 3 the controllersystem is not included. A tachometer, not shown in the diagrams, iscoupled to each peristaltic pump and sends information regarding thepump rotation speed to the controller 19 via wires 60 and 58. The pumpflow rates being proportional to the pump rotation speed the tachometersignal always conveys flow rate related information to the controller.As already mentioned in paragraph 51 both peristaltic pumps have beenconsidered to be similar in all respects because this makes it easier tounderstand and operate the system. However the two peristaltic pumps mayalso be different in context with the inner diameter of the peristalticpump tubes 4 and 13 but in such case suitable modifications have to bemade in the controller programming in order to operate the system asdescribed in this manuscript. The controller also regulates the rotationspeed of the two pumps via electrical signals sent through wires 59 and61. The pressure transducer 17 conveys the pressure signal to thecontroller via wires 62. On the basis of a pressure feed back signalreceived from the pressure transducer 17 the controller regulates therotational speed of the inflow pump 5. The outflow pump 14 works atfixed outflow rates and the flow rate of this pump is also regulated bythe controller via suitable electrical signals sent via wires 61. Aprovision exists by which desired values for P and R2 can be fed intothe controller and the values R1, R2 and P can be continuously displayedvia suitable display means incorporated in the controller. Thecontroller can be programmed to perform many special functions relatedto endoscopic surgery.

Method of Operating the Controller Based Version of the Invention:

Again referring to FIG. 2, in context with the present invention at thestart of surgery the surgeon initially selects suitable values forcavity pressure P and outflow rate R2. The said desired values of P andR2 are fed into the controller via suitable input means incorporated inthe controller. The diameter D at the constriction site 8 remains fixedat some pre selected value. The diameter of the constriction site 8 isso chosen that it suits the operational needs of the endoscopicprocedure. When the system shown in FIG. 2 is operated the controller 19instructs the outflow pump 14 via wires 61 to continuously extract fluidout of the body cavity 18 at a desired fixed outflow rate R2. Thus allthrough the surgery the outflow rate remains fixed at R2 irrespective ofany internal or external factors unless intentionally changed by thesurgeon. The cavity pressure is sensed by the pressure transducer 17 anda corresponding pressure feedback signal is sent to the controller viawires 62 on the basis of which the controller regulates the inflow rateR1, via wires 59. After the system is made operational the controller 19gradually increases the inflow rate up to the point where the desiredpreset cavity pressure P is achieved. Let the value of the inflow rateat which the desired cavity pressure is achieved be termed as‘R1.Final’. It is obvious that the value ‘R1.final’ is actuallydetermined by the controller by a pressure feed back mechanism and suchdetermination of the value ‘R1.Final’ is based on the preset values ofR2 and P. The controller is so programmed that once the value ‘R1.Final’is achieved and is maintained for a desired minimum time interval, forexample 10 seconds, after which the controller releases the inflow pump4 from its pressure feedback control mechanism and allow the inflow pump4 to operate on its own at an inflow rate ‘R1.Final’ which wasdetermined by the controller. In this manner the two peristaltic pumpscontinue to work at fixed flow rates to maintain a desired stable cavitypressure. The controller is also programmed that in case the cavitypressure subsequently alters, for example due to intravasation, by adesired minimum preset magnitude and for a desired minimum time, whichmay hypothetically be 10 seconds, the inflow pump 4 again comes underthe pressure feedback control of the controller and a new value of‘R1.Final’ is determined by the controller after which the inflow pump 4is again allowed to be operated without the pressure feedback mechanismat the newly determined ‘R1.Final’ inflow rate. Such sequence of eventscontinue to occur throughout the endoscopic procedure. Taking animaginary example if the total surgical time is 60 minutes then it maybe hypothetically possible to operate the inflow pump independent of thepressure feedback mechanism for 55 minutes and under the control of thepressure feedback mechanism for 5 minutes. However, provision ofoperating the inflow pump 4 under a pressure feedback mechanism allthrough the endoscopic procedure can also be incorporated.

The Advantage of Operating the Inflow Pump Independent of the PressureFeedback Mechanism:

The only reason for operating the inflow pump 4 independent of thepressure feedback mechanism is to avoid unnecessary corrections of minorpressure variations caused by physiological cavity wall contractions.The concept of physiological cavity wall contractions has been explainedin detail under the heading ‘basic physics of cavity distension’. In thepresent invention the physiological variations in cavity pressure areautomatically corrected by the constriction site 8 without the need of acontroller. If the cavity contracts a minute quantity of fluid which ispushed out of the cavity escapes via the constriction site 8 towardspoint 3. It is to be noted that the part of tube 7 between point 8 and 3is at atmospheric pressure thus the fluid which is expelled from thecavity as a result of a physiological contraction escapes through theconstriction site 8 against a zero pressure head, which beingatmospheric pressure. Thus, the transient, insignificant andinstantaneous rise and fall in cavity pressure variations get stabilizedat the desired preset value within a fraction of seconds. Alternativelyif the cavity expands a suitable volume of fluid is sucked into thecavity from the irrigation circuit, such as from the region of point 6,and this is accompanied by a corresponding transient decrease in theflow rate at which fluid is escaping via the constriction site 8 in thedirection of point 3 but if the magnitude of the said physiologicalexpansion is more fluid may even be sucked into the cavity via theconstriction site 8. This implies that the constriction site 8 ishelping in maintaining a stable cavity pressure despite physiologicalcavity wall contractions by suitably varying the magnitude of animaginary fluid flow vector passing through the constriction site 8.Normally the direction of such imaginary vector is always towards point6 while its magnitude constantly varies to take care of the pressurechanges resulting due to physiological cavity contractions. Normally acavity continuously contracts and dilates by approximately the samemagnitudes thus there is no logic to check the minor pressure variationsemanating from the said contractions. Also the opening of theconstriction site 8 does not allow the said physiological cavitypressure fluctuations to cause any significant cavity wall movementexcursions by allowing to and fro movement of flow through its lumen.However, if the said pressure changes are made to be corrected by acontroller, as is done in the prior art systems, the cavity wall mayexhibit significant irregular pressure fluctuations which may result insignificant movement excursions of the cavity wall, thus disallowing apredictably stable mechanical stabilization of the cavity walls.However, in the eventuality of fluid intravasation the fall in cavitypressure drop is relatively more permanent in nature thus needs to becorrected by the controller. As explained in the previous paragraph thecontroller is so programmed that the inflow pump 4 automatically comesunder the pressure feedback control mechanism of the controller in casethe cavity pressure alters by a desired minimum preset magnitude and fora desired preset time interval, thus a new ‘R1.Final’ inflow rate isestablished at which the inflow pump is again allowed to operate withoutthe feedback control of the controller. As a safety precaution aprovision can be made in the controller via suitable input means to fixan upper safe limit for the inflow rate R1 and the cavity pressure Psuch that these safe limits are not exceeded accidentally.

Removing the Outflow Pump

Referring to FIG. 2 the outflow pump 14 can also be totally removed andthe outflow tube 12 may be made to drain directly into the waste fluidcontainer 16. In such a case a permanent constriction can also beincorporated inside the out flow tube 12. A vacuum source can also beattached to the waste fluid collecting container 16. However theembodiment described in this paragraph is much inferior to the system ofthe proposed invention and it is for this reason that schematic diagramsrelated to this inferior embodiment have not been included in thismanuscript.

A Variable Constriction Site

In context with the system shown in FIG. 2 it is also possible to have asystem in which the cavity pressure is maintained and regulated bycontinuously varying, by the help of a controller, the diameter D at theconstriction site 8. The housing tube having the constriction site issubstantially responsible for dampening the pressure pulsation orminimizing the turbulence inside the cavity. It however may not provideany substantial dampening to the pressure pulsation caused by theworking of the inflow or outflow pumps. The diameter D at theconstriction site 8 could also be intermittently regulated by acontroller as and when required for example in the eventuality of fluidintravasation or extravasation thus implying that the diameter D shallbe free from the influence of the controller for most of the time andshall be brought under the influence of the controller only when neededand that also for only a small part of the total surgical time. Such aconcept has been described in great detail in the previous paragraphs incontext with FIG. 2. In the variable constriction system proposed inthis paragraph both pumps 5 and 14 would always operate at desired butfixed flow rates and the cavity pressure would be regulated only byvarying the diameter D at the constriction site 8. At the start of thesurgery the inflow and outflow rates would be set by feeding suitableflow rate values into the controller after which the controller wouldnot influence or regulate the said two pumps and the cavity pressurewould be maintained only by varying the diameter D at the constrictionsite 8. In order to vary the diameter at the constriction site 8 asuitable electromechanical devise such as a solenoid operated devisecould be installed over the housing tube 7. Such a devise is not adevise which would either totally close or totally open the lumen of thepipe. By the help of the said devise the lumen diameter would be variedin a controlled manner and not just by totally opening or totallyclosing the lumen. The said devise could comprise of a long coilcontaining a movable long cylindrical magnet and this magnet piece bypressing over the tube, would vary the inner diameter of the tube. Whencurrent passes through such coil the magnet piece would either be pulledin or pushed out depending upon the direction of the current and thepolarity of the magnet and the force which the said long cylindricalmagnet piece could apply over the plastic tube would depend upon thecurrent density passing through the coil or in simpler terms the amountof electrical energy supplied to the coil. In context with the presentparagraph the controller shall regulated the amount of electrical energysupplied to the coil such that the magnetic rod presses over the tubewith an adequate force and the inner diameter of the pipe would dependupon such force. Thus the inner diameter of the tube shall be a functionof the current density. The system efficiency of this particularembodiment of the proposed invention could be greatly enhanced byincorporating a system of pump synchronization as described in the nextparagraph. The variable constriction site as described in this paragraphhas not been included in any of the figures only to keep the manuscriptsimple.

A System of Pump Synchronization

As discussed in the preceding paragraphs the system of the proposedinvention as shown in FIGS. 2 and 3 helps in considerably reducingcavity fluid turbulence. However the two perictaltic pumps createpressure pulsations which in turn causes some turbulence inside thecavity. A method shall now be described to minimize such turbulence bysynchronizing the two peristaltic pumps on a single common centralshaft. The two positive displacement inflow and outflow pumps 5 and 14,which are preferably peristaltic pumps, can be attached, that ismounted, on a common central driving shaft which is in turn rotated by acommon single motor. Referring to FIG. 7, the two peristaltic pumps 5and 14 are mechanically coupled to a common driving shaft 26 which isdriven by the motor 35. The motor 35 can be any suitable motor forexample a DC electric motor. Points 27 and 28 refer to the mechanicalcoupling sites between the common driving shaft 26 and the pumps 5 and14. In FIG. 7 the rollers of the peristaltic pump 5 have been referredto as 20, 22 and 24 and the symbolic attachment of these rollers withthe central axis point 27 is denoted by lines 29, 30 and 31respectively. The rollers of the peristaltic pump 14 have been referredto as 21, 23 and 25 and the symbolic attachment of these rollers withthe central axis point 28 is denoted by lines 32, 33 and 34respectively. The inner diameter of tube 4 related to the inflowperistaltic pump 5 has to be greater than the inner diameter of tube 13related to the outflow pump 14 and the same had also beendiagrammatically depicted in FIG. 7. The motor 35 rotates the commondriving shaft 26 in the direction of the curved arrow located at theextreme right side of the diagram in FIG. 10. The common driving shaft26 being mechanically coupled to the two peristaltic pumps, rotatesthese pumps in the direction of the two curved arrows related to eachpump. In FIG. 7 the rollers of the two peristaltic pumps are seenlocated at 12 'O clock, 4 'O clock and 8 'O clock positions respectivelyfor both pumps. Let us consider rollers 20 and 25 related to the inflowand the outflow pumps respectively. Let it be assumed that when themotor 35 rotates the diving shaft 26 then it takes a time T for theroller 20 of the inflow pump 5 to move from its initial 12 'O clockposition to 4 'O clock position. Let it also be assumed the outlet endof the inflow pump 5 to be situated at 4 'O clock position. As the twopumps are mechanically coupled to the common shaft 26 the correspondingroller 25, related to the outflow pump 14 also takes the same time T tomove from its initial 8 'O clock position to the 12 'O clock position.Let it also be assumed the inlet end of the outflow pump 14 is locatedat the 8 'O clock position. While the roller 20 moves from the 12 'Oclock position to the 4'O clock position a positive pulse having amagnitude M1 tends to be created inside the tissue cavity. While theroller 25 moves from the 8 'O clock position to the 12 'O clock positiona negative pressure pulse having a magnitude M2 tends to be createdinside the tissue cavity. As the two peristaltic pumps are synchronizedthe said positive and negative pressure pulses having magnitudes M1 andM2 tend to cancel or negate the effect of each other and the magnitudeM3 of the resultant pressure pulse is equal to M1-M2. The magnitude ofthe resultant pressure pulse can be made almost negligible by suitablemechanical adjustments of the spatial alignment of the rollers of thetwo peristaltic pumps. The roller 20 related to the inflow pump and theroller 25 related to the outflow pump have been termed as ‘correspondingrollers’ because while roller 20 of the inflow pump creates a positivepressure pulse inside the cavity by pushing fluid into the cavity theroller 25 creates a negative pressure pulse inside the cavity byactively extracting fluid out of the cavity. A similar example can alsobe proposed for corresponding rollers 24 and 23, and rollers 22 and 21.In the system shown in FIG. 10 the spatial alignment of rollers relatedto both the pumps can be adjusted experimentally in order to achieve theminimal possible fluid turbulence and once the minimum desiredturbulence level is achieved the relative orientation or alignment ofthe corresponding rollers is not changed. It is clear that the magnitudeof the said ‘net pressure pulse’ depends upon M2, M3 and the relativeinstantaneous spatial position of the said corresponding rollers. If theinflow and the outflow pumps are not synchronized via the common shaft26 or if the pumps run at different RPM's the M1 and M2 can never cancelor negate the effect of each other thus leading to fluid turbulence.Thus by synchronizing the two peristaltic pumps via the common drivingshaft 26 the fluid flow through the cavity can be made almost pulselessand very close to laminar or a streamline flow.

Thus by synchronizing the two pumps cavity fluid turbulence canminimized or almost negated. If the two pumps rotate at different RPM'sthen the relative corresponding positions of the rollers of the twopumps constantly keeps on changing which gives rise to unwanted cavityfluid turbulence. However in the ‘synchronized pump system’ described inthis paragraph the flow rates of the inflow and the outflow pumps cannotbe altered independent of each other and if the cavity pressure needs tobe varied without changing pump RPM's then the same is possible onlyvarying the diameter D of the constriction site 8.

A Method to Dampen the Pressure Pulsations of a Peristaltic Pump

The ‘system of pump synchronization’ discussed in the previousparagraphs helps in reducing or dampening the pressure pulsationscreated by the two peristaltic pumps thereby it helps in reducing theturbulence inside the tissue cavity. However such system of attachingthe two peristaltic pumps on a single common driving shaft ispractically difficult and it does not allow the two pumps to be runindependently of each other thus an easier method of dampening thepressure pulsation of a peristaltic pump is being proposed and the sameshall henceforth be referred to as ‘pressure pulse dampening system’while the other method is being termed as ‘pump synchronization system’.

Referring to FIG. 4 the fluid pressure, such as at a point 6, ispulsatile in nature because the peristaltic pump 5 constantly pushesfluid via its outlet end in the form of a pulsed manner and not in acontinuous manner. Hypothetically assuming that the pump 5 rotates atfixed RPM then in that case the frequency of such pulsations wouldremain uniformly the same all through the operation of the pump. If agraph is plotted for the said pulsations, by relating the fluid pressureto the ‘Y’ axis and the time to the ‘X’ axis, then such graph would havea uniform shape having positive and negative pressure swings of apredictably fixed amplitude and fixed frequency. It is to be noted thatas the pump RPM is increased the frequency as well as the amplitude ofthe said pressure swings also increase. The said pulsations are producedbecause each time any one roller of the peristaltic pump comes inapposition with a fixed point, for example the outlet end of theperistaltic pump, some fluid is pushed out from the outlet end of thepump in the form of a bolus. The wave form of such pulsations need notbe sinusoidal, but for the sake of an easier understanding let the saidwaveform be hypothetically assumed to be sinusoidal in nature. Asalready stated, if the pump RPM increase then along with the frequencythe amplitude of the said waveform also increases. When the pump 5rotates in the direction of the curved arrow fluid tends to accumulatein tube 9 and in tube 7 between points 6 and 8, and let this cavityconsisting of tube 9 and the said part of tube 7, into which the fluidtends to accumulate, be termed as ‘fluid accumulation region’. Inphysical terms the said pressure pulsations are produced because thefluid tends to accumulate in the ‘fluid accumulation region’ in the formof regular pulses wherein each pulse corresponds to a fixed volume offluid pushed by a roller into the ‘fluid accumulation region’ in theform of a bolus of fluid. Thus the motion of each roller wouldcorrespond to one complete sinusoidal pressure wave. The movement of asingle roller in relation to a fixed point such as the outlet end of thepump can be hypothetically divided into three parts, that is, part onewhen the roller approaches the said point, part 2 when the roller is inapposition with the said point and part 3 when the roller moves awayfrom the said point. Let the parts 1, 2 and 3 be collectively termed as‘single roller movement’ and the time taken to accomplish the said‘single roller movement’ be termed as ‘single roller time’. Assuming thepressure waveform to be a sinusoidal curve, each ‘single rollermovement’ corresponds to one complete sinusoidal pressure waveformconsisting of a positive pressure surge followed by a negative pressuresurge or vice versa. Also the time period of the assumed sinusoidal waveform would be equal to ‘single roller time’. If during the positivepressure surge an adequate volume of fluid is removed from the ‘fluidaccumulation region’ and during the negative pressure surge the sameadequate volume of fluid is again added back into the ‘fluidaccumulation region’ the sinusoidal nature of the pressure waveformcould get dampened and the resultant waveform would get transformed intoan almost straight line curve. The resultant waveform couldtheoretically be an absolute straight line if the wave form associatedwith the said process of adding and removing adequate volumes of fluidfrom the ‘fluid accumulation region’ absolutely resembled with the waveproduced as a result of the pulsatile flow of the peristaltic pump andthe phase difference between the two waves was exactly 180 degreeshowever this may not be achieved in practical situations. However asubstantial dampening of the resultant waveform could be practicallyachieved if a syringe system was synchronously coupled with the inflowperistaltic pump 5 and the single outlet end of the said syringe systemwas connected with the ‘fluid accumulation region’. Referring to FIG. 8,this figure is the same as FIG. 4 except that a said syringe system 38has been included. The syringe system 38 consists of a piston 39 denotedby a shaded area. The piston 39 moves up and down inside a cylinder 43while making a watertight contact with the inner walls of this cylinder43. One end of a straight rod 40 is connected to the piston while theother end of this rod 40 is connected to a coupling mechanism 37 housedon a common shaft 36. The coupling mechanism 37 and the peristaltic pump5, both are attached on to a common shaft 36. The coupling mechanism 37is so designed that it converts the rotary motion of the shaft 36 into alinear up down motion of rod 40 which is ultimately manifested as an updown movement of piston 39 inside the cylinder 43. The up down motion ofthe rod 40 is denoted by arrows 41 and 42. Thus the shaft 36 is a commonshaft which mechanically operates both, pump 5 as well as the syringesystem 38. The direction of rotation of the shaft 36 is denoted by acurved arrow located at the right end of the shaft 36. The syringesystem 38, as the name suggests, resembles a hypodermic syringe used forgiving injections to patients. Obviously, the syringe system 38 has onlyone single opening 44. A tube 45 extending between the opening 44 andthe inflow tube 10 connects the syringe system to the inflow tube 10.Tube 10 is a part of the said ‘fluid accumulation region’ described inthis paragraph. Thus the syringe system can be considered to beconnected with the said ‘fluid accumulation region’. The opening 44 canbe referred to as an ‘outlet end’ or an ‘inlet end’ because the syringesystem can push as well as pull fluid from the ‘fluid accumulationregion’. However for the sake of convenience henceforth the opening 44shall be termed as the outlet end of the syringe system 38. The couplingmechanism 37 is so designed that the vertical movements of the syringesystem can be accurately synchronized with the rotary motion of theperistaltic pump 5. The piston 39 can move up>down>up or down>up>down,depending upon the initial position of the piston at the start of themotion and let each such movement of the piston be termed as a ‘completepiston movement’. The coupling mechanism 37 is so designed that whilethe peristaltic pump 5 rotates by 360 degrees the syringe systemcorrespondingly exhibits ‘complete piston movements’ which are equal tothe number of the rollers of the peristaltic pump. Thus for aperistaltic pump which has three rollers then for each 360 degreesrotation of the peristaltic pump the syringe system exhibits three‘complete piston movements’ while for a peristaltic pump with fourrollers four ‘complete piston movements’ would occur for each 360 degreerotation of the peristaltic pump. The syringe system is synchronizedwith the peristaltic pump via the coupling mechanism 37 in such mannerthat while a roller of the peristaltic pump produces a positive pressurepulse the syringe system extracts fluid out from the ‘fluid accumulationregion’ and while the same roller produces a negative pressure pulse thesyringe system pushes an equivalent volume of fluid back into the ‘fluidaccumulation region’. In order to dampen the pulsations of theperistaltic pump, besides mechanically synchronizing the syringe systemwith the peristaltic pump the volume of fluid pulled in or pushed out ofthe syringe system corresponding to each upward or downward movement ofthe piston also has to be adjusted accurately, and the same may be donemanually by a ‘hit and try method’. The volume of fluid pulled in orpushed out by the syringe system depends upon the linear movementexcursion of the piston 39. Also the magnitude of the downward pistonexcursion is equal to the magnitude of the upward piston excursion, thusthe volume of fluid pushed out is always equal to the volume of fluidpulled in during each downward or upward movement. Thus the couplingmechanism 37 has two functions, synchronization of the syringe systemwith the peristaltic pump and adjusting the volume of fluid pulled in orpushed out by the syringe system for each upward or downward movement ofthe piston. The synchronization and the determination of the said volumeto be pushed out or pulled into the syringe system are done manuallysuch that a substantial dampening of the pressure pulsations is achievedand once this is achieved the synchronization at the level of thecoupling 37 is never again disturbed and the volume of fluid pulled inor pushed out of the syringe system for each movement excursion is alsonot changed thereafter. After the coupling 37 is adjusted with respectto synchronization and the volume of fluid to be pulled in and pushedout, the peristaltic pump pulsations shall continue to remain dampenedindependent of the peristaltic pump RPM and the nature of rotation, thatis fixed or variable RPM. In simpler terms the peristaltic pumppulsations would continue to remain dampened even at a high pump RPM.Also the point at which the syringe system 38 is connected to the said‘fluid accumulation region’, for example the inflow tube 10, then theposition of such a point should also not be changed thereafter becausethis may bring about a phase difference between the waveform related tothe peristaltic pump pulsations and the waveform related to the syringesystem pulsations, thus the resultant dampening could no longer besatisfactory. Also preferably the outlet tube 45 of the syringe systemshould be connected as close to the outlet end of the inflow peristalticpump as possible.

The coupling 37 can be compared to some extent with the conventional CAMsystem present in automobile engines. Any specific mechanical design forthe coupling 37 is not important, it is the resultant function of thecoupling 37 with respect to the piston movement, as already described,which is important. The coupling 37 can have many mechanical designs.FIG. 9 shows one such possible mechanical design for the coupling 37. InFIG. 9 a small length of the common shaft 36, which is related to thecoupling 37, has been made of triangular shape as seen in its crosssectional view and the same is labeled as 49. Let this triangular part49 be termed as the ‘piston coupler’. The edges of the piston couplerare shown sharp however they could preferably be rounded to suit variousoperational needs. Similarly the size of the ‘piston coupler’ could alsobe increased or decreased in order to decrease or increase the volume offluid displaced by the cylinder during a downward or upward movement ofthe piston. The central axis point of the ‘piston coupler’ is denoted bypoint 48. In case the dimensions of the ‘piston coupler’ are chosen tobe relatively larger than the dimension of the common shaft 36, thepoint 48 could also represent the point at which the common shaft 36passes through the ‘piston coupler’ and in such a situation the ‘pistoncoupler’ 49 could be manually rotated on the common shaft 36 in aclockwise or anti clockwise direction and then locked mechanically at aposition which provides the most accurate synchronization. The springs46 and 47 extending between the inner walls of the cylinder and thepiston exert a constant and substantially large upward pull on thepiston 39 which causes the rod 40 to constantly be in apposition withthe ‘piston coupler’ 49. The springs can be one or more than one innumber and the springs can also be substituted by any other mechanicalmeans also which provide an active upward movement of the piston. The‘piston coupler’ 49 is assumed to be able to apply a substantially largedownward force on the piston 39 via rod 40 such that a correspondingtransient negative fluid pressure pulse inside the cylinder can betotally neglected in the face of the said large substantial downwardforce. Similarly the springs 46 and 47 are capable of pulling up thepiston with a substantially large force such that a correspondingtransient positive fluid pressure pulse inside the cylinder could betotally neglected. The idea is that the downward movement of the pistonshould not be aided by the negative pressure pulse inside the cylinder,this downward movement should be an active movement for which energy isto be derived from the springs from the shaft 36. Similarly the upwardmovement of the piston should not be aided by the positive pressurepulse inside the cylinder, this upward movement should be an activemovement for which energy is to be derived from the springs 46 and 47.The energy for the said upward movement of the piston could also bederived from the shaft 36 if suitable mechanical provision facilitatingan active upward movement of the piston could be provided at the levelof the coupling 37.

It is important to note that it is not mandatory to use the said‘pressure pulse dampening system’ with a peristaltic pump only as, withsuitable mechanical modifications, the ‘pressure pulse dampening system’could be used beneficially with any type of a positive displacementpump.

The ‘pressure pulse dampening system’ could also be a mechanism like the‘piston coupler’ shown in FIG. 9 whose rounded edges could directlyimpinge on a suitable area situated on the outer surface of the ‘fluidaccumulation region’ in a uniform synchronized manner, as described,such that this results in continuous uniform synchronized variations inthe total volume capacity of ‘fluid accumulation region’. The saidsuitable area on the outer surface of the ‘fluid accumulation region’could be a membrane made consisting of a strong resilient polymericmaterial having an adequate elasticity. The said membrane should also besufficiently thick and should have an adequate elasticity such that anoutward movement of such membrane, a movement related to the upward pullby the said springs, applied a substantially larger force in comparisonto force related with the transient corresponding pressure pulse.

A ‘pressure pulse dampening system’ presently being described for theinflow pump 5 should be preferably installed on the outflow peristalticpump 14 also in an exactly similar manner as already described. Thus thesaid dampening is possible for both, inflow and outflow pumps or foronly one single pump, the inflow or outflow one. Obviously the overalleffect of the said dampening as perceived inside the tissue cavity 18shall be more if the said dampening is done at the level of both thepumps because the pressure pulsations from both pumps travel to thetissue cavity 18 and thus they need to be dampened at the level of bothpumps. It is also to be noted that ‘pressure pulse dampening system’ isdifferent from the ‘pump synchronization’ system accomplished by housingthe two peristaltic pumps on to a single common shaft, while in the‘pressure pulse dampening system’ both the peristaltic pumps are housedon separate shafts. ‘Pump synchronization’ is more difficult to achievewhen compared to the ‘pressure pulse dampening system’, however the twomethods can also be utilized simultaneously but in that case both theperistaltic pumps shall have to be attached on to the same commondriving shaft.

In FIG. 1 the inflow 38 and the outflow 55 syringe systems have beenshown synchronized with the inflow and outflow peristaltic pumps 5 and14 respectively. In the outflow syringe mechanism the common shafthouses the coupling 51 which moves the piston 54 via shaft 63 inside thecylinder 64 whose outlet opening 56 is connected to the outflow tube 12via tube 57. The coupling system shown in FIG. 9 would be applicable tothis outflow syringe system also.

The pressure dampening mechanism described in the present invention isan active pressure dampening system and not a passive dampening system.The Applicants have realized that only active pressure dampening systemsas discussed above provide substantial dampening to the pressurepulsation caused by the peristaltic pumps and relying on passive factorssuch as the inherent resistance to the flow of the liquid etc do notprovide any effective pressure dampening. Further, the pressuredampening system may not provide any substantial dampening to thepressure pulsation caused by the physiological contractions of thecavity walls.

A System of Incorporating Multiple Peristaltic Pump Tubes

In the preceding parts of the manuscript the two peristaltic pumps 5 and14 are shown to have one single tube each, that is tubes 4 and 13respectively, which come in contact with the rollers of the peristalticpumps. Arbitrarily referring to the inflow pump 5,${R\quad 2} = {\frac{\pi\quad \times B^{2} \times L}{4} \times {RPM} \times 2}$where R2=Flow rate of pump 5, B=inner diameter of the peristaltic pumptube 4, L=length of tube 4 and RPM=revolution per minute of pump 5. Ifthe value B is doubled then for the same RPM the flow rate R2 doubles.Similarly if L doubles then also for RPM the flow rate R1R2 doubles.However keeping in mind the mechanical constraints the values B and Lcannot exceed a certain practical value. However if two tubes like tube4 are used in parallel in the pump 5 then the mathematical expressionfor the flow rate could be written as follows:${R\quad 2} = {\frac{\pi \times B^{2} \times L}{4} \times {RPM}}$This implies that if two peristaltic pump tubes are used instead of onesingle tube then the flow rate becomes double for the same RPM and ifthree tubes are used then the flow rate becomes three times and so on.The frequency of the ‘pressure pulsations’ created by a peristaltic pumpis directly proportional to the pump RPM. The said ‘pressure pulsations’are undesirable thus it is helpful to keep their frequency as minimal aspossible if the flow rate is not compromised. Thus this system ofincorporating two or more peristaltic pump tubes helps in attaining ahigher flow rate for a relatively lesser RPM. It is but obvious that thesaid two or more than two parallel tubes are connected to each other atthe inlet and the outlet ends of the peristaltic pump.Determination of the Instantaneous Real Time Rate of Fluid Intravasation

Fluid intravasation is a process by which the irrigation fluid entersinto the patient's body system and if excess volume of fluid isintravasated it can be dangerous to the patient's life. Thus, keeping inmind surgical safety, it is extremely important to constantly know therate at which such intravasation occurs so that corrective surgicalmeasures can be taken before a dangerous volume of fluid intravasates.The inventors propose that one fluid flow rate sensor each beincorporated in the inflow tube and the outflow tube. Referring to FIGS.1, 2 and 3 the inflow flow rate sensor should be located in the inflowtube 10 anywhere between the inlet port of the endoscope and the pointat which the distal end of the constriction site housing tube 7 isconnected to the inflow tube, such as point 6. Such a flow rate sensorwould measure the rate at which fluid enters into the tissue cavity 18and the same is being termed as ‘cavity inflow rate’. Obviously the‘cavity inflow rate’ is the true inflow rate for the tissue cavity.Similarly the outflow flow rate sensor should be located anywhere in theout flow tube between the outflow port of the endoscope and the inletend of the outflow peristaltic pump 14 or any other outflow positivedisplacement pump. However if an additional or optional constrictionsite housing tube 17 is also connected to the out flow tube 12 as shownin FIG. 6 then the outflow flow rate sensor should be located betweenthe outflow port of the endoscope and the point at which the proximalend of the constriction site housing tube 17 is connected to the outflowtube 12. The outflow flow rate sensor measures the rate at which fluidis extracted from the tissue cavity which is the same as R2 that is theflow rate of the outflow pump. Now the real time rate of fluidintravasation, being termed as R3, can be determining by subtracting R2from the ‘cavity inflow rate’, the mathematical expression for the samebeing can be written as R3=Cavity inflow rate−R2. The said flow ratesensors should be accurate, reliable, easy to install and should nothave any movable parts. The inventors suggest that a the said sensorcomprise of a heating coil in physical contact with a metal plate forheating the same and a temperature sensor placed in contact with themetal plate, the temperature of the metal plate being a function of thefluid flow rate. The said flow rate sensors are electrically connectedwith a micro-controller which automatically subtracts R2 from the‘cavity inflow rate’ to give the value R3. The value R3 can also befurther integrated with respect to time to give the total volume offluid intravasated over a certain time interval. The said temperaturerelated flow rate sensor could be a ‘hot wire anemometer’.

The proposed invention can also be used to impart endoscopic trainingskills by the help of endoscopic experimental models based on thepresent invention. Also use and scope of the present invention is notlimited to human tissue cavities and it may be used for performingmultiple endoscopic procedures in animal tissue cavities also and alsofor imparting training in endoscopic surgeries related to animal tissuecavities.

It is believed that the foregoing description conveys the bestunderstanding of the objects and the advantages of the presentinvention. It will be understood by those skilled in the art thatnumerous improvements and modifications may be made to the embodimentsof the invention disclosed herein without departing from the departingfrom the spirit and scope thereof.

THE Invention is Unique

There is no other prior art system in which the amplitude of pressurepulsations produced by a positive displacement, like a peristaltic pump,could be minimized to a negligible level. Also the concepts of ‘pressurepulse dampening system’, ‘system of pump synchronization’, determinationof the instantaneous rate of fluid intravasation by using two hot wireanemometers and the concept of installing two or more peristaltic tubesin parallel have not been described in any prior art system

The Heart and Soul of the Invention

The ‘pressure pulse dampening system’ using a syringe mechanism is theheart and soul of the invention without which the invention cannotexist.

Advantages of the Proposed Invention

The proposed invention makes endoscopic procedures extremely safe,simple, more accurate and easy to perform. The proposed invention helpsthe surgeons to perform endoscopic surgeries with greater safety andconfidence especially in the initial phase of their learning curve. Alsoa distending system based on the proposed invention can be used inmultiple endoscopic procedures thus reducing the financial burden on thehospital and the patient. The advantages of proposed invention aresummarized in the following table along with the correspondingdisadvantages of the prior art systems: ADVANTAGES OF THE DISADVANTAGESOF THE PRESENT INVENTION: PRIOR ART SYSTEMS: It is possible to reducethe This is not possible in amplitude of the pressure pulsations anyprior art system. created by a positive displacement pump to an almostnegligible magni- tude irrespective of the pump RPM. It is possible tominimize cavity This is not possible in fluid turbulence to almostnegligible any prior art system. levels. It is possible to create andmaintain This is not possible in any desired precise tissue cavity anyprior art system. pressure for any desired precise fixed outflow rateincluding a zero outflow rate. The instantaneous real time rate of Suchfeature is not fluid intravasation into the patient's present in anyprior body is constantly known by using a art system. hot wireanemometer type of a flow rate sensor. The instantaneous real time rateof This is not possible in fluid intravasation into the patient's anyprior art system. body can be determined even mechanically without usinga controller and any type of fluid flow rate sensors. A predictablyconstant any desired This is not possible in fluid pressure can bemaintained any prior art system. inside a tissue cavity for indefinitetime. A predictably constant any desired This is not possible in fluidpressure can be maintained any prior art system. inside a tissue cavityfor indefinite time despite physiological cavity wall contractions. Apredictably constant clear This is not possible in endoscopicvisualization is possible. any prior art system. It is possible toachieve a This is not possible in predictably stable mechanical anyprior art system. distension of the cavity walls. It is possible tomaintain any desired This is not possible in precise and high cavitypressure any prior art system. without increasing the ‘maximum possiblefluid intravasation rate’. It is possible to easily and quickly This isnot possible in change over from one type of any prior art system.irrigation fluid to a different type of irrigation fluid during anendoscopic procedure in any desired short period of time such that thecavity pressure does not change during such maneuver.

CONCLUSION

The proposed invention is novel and unique. The invention relates notonly to increasing surgical efficiency in certain endoscopic proceduresbut it also helps in preventing human morbidity and human mortality inmany endoscopic procedures. Thus the proposed invention is extremelyuseful for entire mankind.

1. A system for distending body tissue cavities of subjects bycontinuous flow irrigation during endoscopic procedures the said systemcomprising: a fluid source reservoir containing a non viscousphysiologic fluid meant for cavity distension; a fluid supply conduittube connecting the fluid source reservoir to an inlet end of a variablespeed positive displacement inflow pump and an outlet end of the saidinflow pump being connectable to an inflow port of an endoscopeinstrument through an inflow tube for pumping the fluid at a controlledflow rate into the cavity, the flow rate at which the fluid enters intothe cavity via the inflow tube being termed as the cavity inflow rate;an inflow pressure transducer being located anywhere in the inflow tubebetween the outlet end of the inflow pump and the inflow port of theendoscope; an inflow pressure pulsation dampening means connected to theinflow tube for dampening the pressure pulsations inside the cavitycreated by the positive displacement inflow pump, an outflow port of theendoscope being connectable to an inlet end of a variable speed positivedisplacement outflow pump through an outflow tube for removing the fluidfrom the cavity at a controlled flow rate, the flow rate of the saidoutflow pump being termed as the cavity outflow rate, an outflowpressure pulsation dampening means connected to the outflow tube fordampening the pressure pulsations inside the cavity created by thepositive displacement outflow pump; an outlet end of the outflow pumpbeing connected to a waste fluid collecting container, and a housingtube having a controllable constriction site is being provided betweenthe fluid source reservoir and the inflow tube such that the sameby-passes the inflow pump; wherein housing tube provides a route for anyexcess fluid being pumped by the inflow pump to bypass the inflow pumpand go back to the fluid supply tube or the fluid source reservoir,thereby minimizing turbulence inside the cavity and maintaining thecavity pressure at a stable value despite physiological contractions ofthe cavity wall.
 2. A system as claimed in claim 1, wherein the fluidsource reservoir containing the non-viscous physiologic fluid ismaintained at atmospheric pressure or at a pressure greater than theatmospheric pressure.
 3. A system as claimed in claim 1, wherein aproximal open end of the fluid supply tube is connected to the fluidsource reservoir and a distal end of the tube is connected to the inletend of the variable speed positive displacement inflow pump.
 4. A systemas claimed in claim 3, wherein the proximal open end of the fluid supplytube is constantly and completely immersed in the fluid sourcereservoir.
 5. A system as claimed in claim 1, wherein a proximal end ofthe inflow tube is connected to the outlet end of the variable speedpositive displacement inflow pump and a distal end of the inflow tubebeing connectable to the inflow port of the endoscope instrument.
 6. Asystem as claimed in claim 1, wherein the variable speed positivedisplacement inflow pump is selected from the group comprisingperistaltic pump, piston pump, gear pump, diaphragm pump and plungerpump.
 7. A system as claimed in claim 6, wherein the variable speedpositive displacement inflow pump is a peristaltic pump.
 8. A system asclaimed in claim 1, wherein the housing tube is releasably providedbetween the fluid source reservoir and the inflow tube to enablereplacement of the housing tube with yet another housing tube having adifferent diameter at the constriction site to suit the operational needof the endoscopic procedure.
 9. A system as claimed in claim 1, whereina proximal end of the housing tube is connected to the fluid supply tubenear its distal end close to the inlet port of the inflow pump.
 10. Asystem as claimed in claim 1, wherein a proximal end of the housing tubeempties directly into the fluid source reservoir and is constantly andcompletely immersed in the fluid source reservoir.
 11. A system asclaimed in claim 1, wherein a distal end of the housing tube isconnected to the inflow tube near its proximal end close to the outletend of the inflow pump.
 12. A system as claimed in claim 1, wherein thehousing tube is provided with a clamping means at the constriction siteto enable the user to vary the diameter of the housing tube at theconstriction site to suit the operational needs of endoscopicprocedures.
 13. A system as claimed in claim 1, wherein the diameter ofthe housing tube at the constriction site is in the range of 0.001 mm toa maximum value which is less than the overall diameter of the rest ofthe housing tube.
 14. A system as claimed in claim 1, wherein thediameter of the housing tube at the constriction site is in the range of0.01 to 2.5 mm.
 15. A system as claimed in claim 1, wherein the inflowpressure transducer is located sufficiently away from the cavity site,preferably near the outlet end of the inflow pump from the practicalpoint of view, such that the fluid pressure measured by the same isalmost equal to the fluid pressure inside the cavity.
 16. A system asclaimed in claim 1, wherein a proximal end of the outflow tube beingconnectable to the outlet port of the endoscope instrument and a distalend of the outflow tube is connected to an inlet end of the variablespeed positive displacement outflow pump.
 17. A system as claimed inclaim 1, further comprising an outflow pressure transducer connectedbetween the proximal end of the outflow tube and the inlet end of thevariable speed positive displacement outflow pump for measuring thepressure in the outflow tube.
 18. A system as claimed in claim 1,wherein the variable speed positive displacement outflow pump isselected from the group comprising peristaltic pump, piston pump, gearpump, diaphragm pump and plunger pump.
 19. A system as claimed in claim18, wherein the variable speed positive displacement outflow pump is aperistaltic pump.
 20. A system as claimed in claim 1, wherein the outletend of the variable speed positive displacement outflow pump isconnected to the waste fluid collecting container through a waste fluidcarrying tube.
 21. A system as claimed in claim 1, further comprising amicro-controller means electrically coupled to the inflow pressuretransducer, the outflow pressure transducer, the inflow pump and theoutflow pump for regulating the operation of the inflow and the outflowpumps.
 22. A system as claimed in claim 1, further comprising a housingtube having a variable size constriction site being provided between theoutflow tube and the waste fluid reservoir.
 23. A system as claimed inclaim 22, wherein the distal end of the housing tube is connected to thewaste fluid carrying tube.
 24. A system as claimed in claim 1, whereinthe fluid supply tube, the inflow tube, the outflow tube and the wastefluid carrying tube are flexible, disposable and are made of polymericmaterial.
 25. A system as claimed in claim 1, wherein the inflow and theoutflow positive displacement pumps are coupled to a common shaft forsynchronously operating these two pumps.
 26. A system as claimed inclaim 24, wherein the housing tube is provided with an electromechanicaldevice, a solenoid, to enable the micro-controller to vary the diameterof the constriction site.
 27. A system as claimed in claim 24, whereinif the inflow and the outflow pumps are coupled to the common shaft, thehousing tube is essentially provided with the micro-controllercontrolled solenoid for varying the diameter of the constriction site.28. A system as claimed in claim 7, wherein the variable speed inflowand outflow peristaltic pumps are provided with 1 to 5 peristaltic pumptubes connected in parallel between the inflow and outflow ends of theperistaltic pumps for reducing the frequency of pulsations in thepressure, the said tubes being connected to each other at the inflow andoutflow ends of the peristaltic pumps, and the said peristaltic pumptubes being the ones which come in contact with the rollers of theperistaltic pumps.
 29. A system as claimed in claim 1, wherein theinflow pressure variation dampening means comprises a single outletsyringe mechanism, the piston of the same being coupled synchronously tothe positive displacement inflow pump through a coupling means and asingle outlet end of the said syringe mechanism being connected to theinflow tube.
 30. A system as claimed in claim 1, wherein the outflowpressure variation dampening means comprises a single outlet syringemechanism, the piston of the same being coupled synchronously to thepositive displacement inflow pump through a coupling means and a singleoutlet end of the said syringe mechanism being connected to the outflowtube.
 31. A system as claimed in claim 1, wherein if the inflow and theoutflow pumps are operated synchronously by coupling them to the commonshaft, the inflow and/or the outflow pressure variation dampening meansare optionally operated synchronously by coupling them to the samecommon shaft.
 32. A system as claimed in claim 1, wherein a fluid flowrate sensor is located in the lumen or wall of the fluid inflow tube formeasuring the cavity inflow rate.
 33. A system as claimed in claim 1,wherein the fluid flow rate sensor is located between the inflow port ofthe endoscope and the location where the housing tube is connected tothe fluid inflow tube.
 34. A system as claimed in claim 1 furthercomprising a fluid flow rate sensor connected between the proximal endof the outflow tube and the inlet port of the variable speed positivedisplacement outflow pump for measuring the cavity outflow rate.
 35. Asystem as claimed in claim 34, wherein the fluid flow rate sensor islocated between the outflow port of the endoscope and a place proximalto the point where the said additional/optional housing tube isconnected to the outflow tube.
 36. A system as claimed in claim 31,wherein the fluid flow rate sensors consists of a heating coil inphysical contact with a metal plate for heating the same and atemperature sensor placed in contact with the metal plate for measuringthe temperature of the said metal plate, the temperature of the metalplate being a function of the fluid flow rate.
 37. A system as claimedin claim 31, wherein the fluid flow rate sensor is a hot wireanemometer.
 38. A system as claimed in claim 31, wherein instantaneousreal time rate of fluid intravasation is determined by electricallyconnecting the inflow and outflow fluid flow rate sensors to amicro-controller.
 39. A system as claimed in claim 1, wherein the fluidsource reservoir, the inflow pump, the tubes, the tissue cavity, and theout flow pump are placed approximately at the same height with respectto a horizontal ground.